The present invention relates to plastic formed products, and more particularly, to plastic formed products which are capable of reducing the amount of residual ash after the plastic formed products are incinerated even under the conditions of a low temperature and a low oxygen concentration due to the incineration-accelerating operation thereof.
Since plastics are capable of being freely molded and have excellent properties of all kinds, a large amount of the plastic formed products are used in industries of all sorts. After accomplishing the intended purposes, these plastic formed products are discarded. It is difficult to decompose physically, chemically or biologically plastic formed products in circulation and since materials of all kinds are used, a significant cost is associated with recovery and recycling plastic products. Due to this cost plastic products are often reclaimed or incinerated. It is well known that major refuse problems are associated with disposal of plastic products.
The plastic formed products are divided broadly into two categories such as (1) industrial materials and durable consumer goods used for a relatively long period (e.g. from several years to several tens of years), and (2) goods used for a short period (e.g. from several days to one year) utilizing serviceability of the product for the required period of time. However, recent changes in life style have resulted in large amounts of single use formed plastic products requiring disposal and as a result the amount of refuse discharged from homes has increased.
In European countries, suppliers should recover the plastic wastes discharged from consumers. It is considered that the plastic wastes are reused as energy resource by generating electricity by utilizing the combustion heat. However, at this time, the plastic wastes in many countries are disposed by the incineration and reclamation.
The present invention will be explained in the following with plastic bags cited as an example.
In supermarkets, large specialty stores and retail shops, plastic bags which are printed or colored for the respective stores are generally supplied to the customers at the sales counters. After these shopping bags are used to carry goods, they are reused in homes as sorting bags, refuse bags or the like.
In conventional disposal of combustible refuse the discarded material is placed in blue or black colored plastic bags. These bags are made of thermoplastic resin, typically polyethylene resin which also contains a pigment. The filled bags are incinerated in an incinerator and after incineration the residual ash together with unburned refuse is used for reclamation.
However, a conventional method of incinerating the combustible refuse has various problems such as air contamination due to NOx generated during incineration, shortage of sites for reclamation into which a large amount of residual ash after incineration and unburned refuse are buried, leakage of a harmful ingredient of residual ash in the reclaimed land, and generation of harmful dioxins. In addition, when a large amount of plastic waste and plastic bag which have a high calorific value is contained in combustible refuse, the temperature in the incinerator is raised so much that the incinerator is broken.
As a method of solving these problems, various methods are proposed. They are, for example, a method of suppressing the generation of NOx by incinerating combustible refuse under the condition of a low oxygen concentration, a method of preventing the breakage of an incinerator due to a rise in temperature by so controlling the incinerator as to be not higher than a predetermined temperature by spraying water during incineration, and a method of insolubilizing the residual ash containing harmful ingredients and cementing it before burying it. In some municipal corporations, it is a duty of the inhabitants to use a translucent plastic refuse bag which contains a large amount of calcium carbonate in place of a conventional refuse bag in order to reduce the amount of refuse and lower the calorific value. It is reported that many municipal corporations appeal to supermarkets and the like for adoption of translucent shopping bags containing calcium carbonate like a refuse bag, because the shopping bags are often reused as refuse bags in homes.
Plastic bags containing iron oxide are also proposed. For example, a method of dispersing a fine ferromagnetic powder in a thermoplastic resin so as to separate plastic wastes by the magnetic action (Japanese Patent Application Laid-Open (KOKAI) No. 52-68247/1977), and a method of producing a plastic bag from polyethylene or polypropylene containing titanium oxide, aluminum oxide, nickel oxide and iron oxide such as ferrous oxide and ferric oxide so as to prevent the generation of an offensive odor from the refuse in the bag (Japanese Patent Application Laid-Open (KOKAI) No. 3-212353/1991) are proposed.
As described above, since the original use of shopping bags is to accommodate goods therein for carrying and they have a function of advertising the supermarket or the retail store which supplies them to the customers, the shopping bags are required to have an excellent color tone and a high mechanical strength, to use no harmful ingredient, and further to be produced at a low cost. It is very difficult to produce a shopping bag which meets all these demands while taking the problem of refuse disposal into consideration.
The suppression of the NOx content generated during incinerating refuse, the prevention of the breakage of an incinerator and a reduction of unburned refuse and residual ash are now in the strongest demand. If the refuse is incinerated under the conditions of a low temperature and a low oxygen concentration, although it is effective for the suppression of the NOx content generated during incinerating refuse and the prevention of the breakage of an incinerator, since the combustion efficiency is lowered, the residual ash and the unburned refuse disadvantageously increase.
If a thermoplastic resin for shopping bags contains a large amount of calcium carbonate, not only is the external appearance bad, but also the mechanical strength is lowered and the calcium carbonate adhered to the film surface is apt to adhere to clothes and commercial goods. In addition, although such bags are effective for the prevention of the breakage of an incinerator due to a high temperature, the amount of residual ash and unburned refuse disadvantageously increases by the amount equivalent to the amount of calcium carbonate added.
The method of Japanese Patent Application Laid-Open (KOKAI) No. 52-68247/1977 is aimed at providing plastics with magnetism by mixing and dispersing a fine ferromagnetic powder such as magnetite with and in the plastics so as to collect the plastics, and a method of Japanese Patent Application Laid-Open (KOKAI) No. 3-212353/1991 is aimed at preventing an offensive odor in the garbage in a plastic bag by adding a gas decomposing material containing at least titanium oxide, aluminum oxide, nickel oxide and iron oxide to polyethylene or polypropylene which constitutes the bag. Japanese Patent Application Laid-Open (KOKAI) No. 3-212353/1991 is silent on the disclosure or suggestion of the technical problem that the combustion efficiency should be maintained and the unburned refuse, residual ash and an harmful ingredient should be reduced as much as possible even under the conditions of a low temperature and a low oxygen concentration.
At the time of incineration of plastic formed products, the plastics are molten and become blocks and combustible volatile compounds vaporize from the plastics in which the solid form thereof is maintained, the necessary amount of oxygen for incinerating the plastic formed products is in short supply, so that harmful unburned refuse sometimes remains or the incineration takes a long time.
Accordingly, provision of plastic formed products which are capable of a high combustion efficiency even if they are incinerated together with combustible refuse, and which are capable of reducing the amount of unburned refuse and residual ash is strongly demanded.
Especially, provision of plastic formed products which are capable of providing an excellent color tone, a high mechanical strength and safety, and which are also capable of maintaining a high combustion efficiency for a long time even if they are incinerated together with combustible refuse, and reducing the amount of unburned refuse and residual ash is strongly demanded.
As a result of studies undertaken by the present inventors so as to meet the demand, it has been found that by mixing and kneading 0.1 to 10.0 wt % of ferric oxide hydroxide particles and/or iron oxide particles with a thermoplastic resin or a thermosetting resin and forming the resultant mixture, the combustion efficiency of the obtained plastic formed products does not lower even if the plastic formed products are incinerated together with combustible refuse under the condition of a low temperature and a low oxygen concentration, and generates only a small amount of unburned refuse and residual ash. The present invention has been achieved on the basis of this finding.